Triangular drive for screen printer

ABSTRACT

Briefly, apparatus embodying the invention includes a rotatable screen holder, adapted to rotate through a segment of a circle, and carrying the screen which has the pattern to be printed, and a horizontal reciprocating support table which carries the workpiece to be printed. A fixed squeegee is disposed in operative relation with the screen. The table and the rotatable screen holder are mechanically coupled together so that they move together, and the work-piece is so positioned that it and the screen come into tangent contact and the pattern is printed as the support plate and screen move together through a printing cycle.

United States Patent 1 1 Larsson 1 1 TRIANGULAR DRIVE FOR SCREEN PRINTER[76| lnventor: Ivar F. Larsson. PO. Box 916.

Wellflect. Mass. 02601 [22] Filed: Oct. 25. 1973 1211 Appl. No: 409,760

[52] 1.1.5. Cl 101/126; 101/116 [51] Int. Cl. B4" 13/16: B4lf15/26 [58]Field ofSearch 101/115. 116.114.124. 101/22,23, 125. 126.118

[56] References Cited UNITED STATES PATENTS 1.856.139 5/1932 Schettler101/22 X 1.995.403 3/1935 Smelling 101/125 2.111.207 3/1938 Denelsbeclc.101/124 2.931.292 4/1960 Ackley 101/37 3.078.792 2/1963 Kerstun 101/35 X3.302.560 2/1967 Edwards et al. 101/114 X 1 1 June 3, 1975 Van DerWindcn 101/118 Stommel 101/22 57 ABSTRACT Briefly. apparatus embodyingthe invention includes a rotatable screen holder. adapted to rotatethrough a segment of a circle. and carrying the screen which has thepattern to be printed. and a horizontal reciprocating support tablewhich carries the work-piece to be printed. A fixed squeegee is disposedin operative relation with the screen. The table and the rotatablescreen holder are mechanically coupled together so that they movetogether. and the work-piece is so positioned that it and the screencome into tangent contact and the pattern is printed as the supportplate and screen move together through a printing cycle.

5 Claims, 8 Drawing Figures 1 TRIANGULAR DRIVE FOR SCREEN PRINTERBACKGROUND OF THE INVENTION Apparatus for silk-screen printingelectronic products is well known and, in general, requireshighprecision operation. Because of this, all such apparatus is of thereciprocating type and includes a horizontal support for the work-piecewhich is moved into position under a silk screen having the pattern tobe printed. After the work-piece is suitably positioned, a squeegeemoves across the screen and forces ink through the screen pattern ontothe work-piece, after which the support is retracted and the work-pieceis removed. The printing pattern is then repeated for anotherwork-piece. It can be seen that considerable useful time is wasted bythe various separate operating steps of such reciprocating apparatus. Inparticular, the total period of time, during which the horizontalsupport moves, is wasted because no useful printing work is performedduring this period.

SUMMARY OF THE INVENTION Briefly, apparatus embodying the inventionincludes a rotatable screen holder and horizontally reciprocablework-piece holder which operate together to perform a printing operationquickly and efficiently with minimal wasted operating time of theapparatus. The screen and work-piece are so positioned that they move atthe same rate with respect to each other during a printing cycle.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a front elevational view ofsilk-screen printing apparatus embodying the invention;

FIG. 2 is a side elevational view, partly in section, of a portion ofthe apparatus of FIG. 1 showing the silkscreen assembly;

FIG. 3 is a front elevational view, partly in section, of a portion ofthe apparatus of FIG. 1 showing .the silkscreen supporting mechanism;

FIG. 4 is a plan view of a portion of the apparatus of FIG. 1;

FIG. 5 is a side elevational view of a portion of the apparatus of FIG.1 illustrating schematically means for removing a printed work-piece;

FIGS. 6 to 8 show schematically the relationship between the printingscreen and work-piece at various stages in a printing cycle.

' DESCRIPTION OF THE PREFERRED EMBODIMENTS In the following descriptionof the invention, it will be seen that some structural elements includeidentical left and right side portions. In some of these cases, the leftand right side portions carry the same reference numeral, with onenumeral being primed.

BROAD PRINCIPLES OF THE INVENTION In its broadest aspects, thescreen-printing apparatus of the invention 10 includes a printing-screenholder which comprises a frame in the form of an are or segment of acircle, as seen clearly in FIG. 2. The screen 30 carrying the pattern 32to be printed is suitably supported on the frame so that its printingsurface also defines an arc of a circle. The frame 20 is rotatablymounted on a horizontal shaft 40.

A horizontally reciprocatory table 50 is mounted adjacent to and beneaththe screen 30 and frame 20, and the frame 20 and the table 50 arecoupled together so that, in a printing cycle, as the table moves in adirection into the paper, as seen in FIG. I, or from left to right asseen in FIG. 2, the frame pivots about the shaft 40. This movementcauses the screen 30 to rotate through an arc of a circle.

The table 50 also carries a work holder 60 for supporting a work-piece70, the work holder being horizontally movable with the table and alsovertically reciprocable to raise the work-piece into operating positionwith respect to the screen, and so that the workpiece is directly incontact with the screen during a printing operation. The screen andwork-piece are positioned so that they move at the same speed withrespect to each other. The apparatus 10 also includes a squeegee mountedinside the frame 20 and adapted to squeeze printing ink over the screenas the screen rotates in operation of the apparatus.

In the beginning of a cycle of operation of the apparatus 10, asdescribed briefly above, the table 50 is retracted and the screen holderframe 20 is positioned at the maximum forward or clockwise position,clockwise as seen in FIG. 2. As the parts begin to move, the table 50moves to the right, the frame 20 rotates counterclockwise, and the workholder 60 rises to bring the work-piece 70 into printing position, and,as the patterned area in the screen 30 reaches the work-piece, thepattern is printed thereon by the squeegee. The work-piece is thenejected as the table and screen begin to retract. As the table andscreen return to their starting position, the work holder movesdownwardly to a position at which it receives another work-piece, andthe apparatus is ready for another printing operation.

DESCRIPTION OF A DETAILED EMBODIMENT OF THE INVENTION Referring to thedrawings, the screen-printing apparatus 10 includes a floor-mountedtable having a top surface 100, to which is secured a second supporttable spaced therefrom a suitable distance and supporting some of theoperating parts of the apparatus. The apparatus 10 includes a controlconsole and a pair of spaced-apart, rigid support members 130, 132, allsuitably secured to the second support table 110.

The screen-carrying frame 20 is disposed between the rigid supportmember 130, 132 and is constructed as an are or segment of a circle. Inone suitable arrangement, the frame 20 comprises essentially twoidentical side plates 140, and suitable connecting members including ahorizontal connecting frame portion 150. The side plates 140, 140' aregenerally triangular in form and include two straight arms 160, 162 anda curved connecting base portion 164 (FIG. 2). The connecting frameportion extends between the apex of the triangle formed by each sidepiece, and a horizontal bore 152 is formed through this portion of theframe to receive the horizontal shaft 40 on which the frame 20 pivots orrotates.

The screen 30 may be supported on the frame 20 in any suitable manner.In one suitable arrangement, shown in FIG. 3 but not in FIG. 1, theinner wall of the base portion 164 of each side plate 140, 140 of theframe 20 includes an inwardly projecting L-shaped portion 165 whichextends along the base portion and follows the curvature thereof. TheL-shaped portion includes a vertical wall 167 having a top surface onwhich is seated, in order, a protective shim 168, the screen 30, and abacking bar 169. The screen 30 is directly secured to the first backingbar 169 by means of screws 172. The screen bears against the backing bar169', and it is secured to a third adjustable backing bar 173 whoseposition with respect to the bar 169' is adjustable by means of screws175 whereby lateral tension on the screen can be adjusted and it can bedrawn taut betwee.. the side plates 164, 164. The backing bars 169, l69and the screen 30 are held in place on the curved base portions 164,164' of the side frames in any suitable manner, for example, by means ofspring-biased toggle clamps 176 built into the curved members 164, 164',as illustrated schematically in FIG. 3.

The frame 20 is also provided, for example, on the outer surface of eachof the curved side plates 140, 140, with means for rotating the frame,for example, a sector of a gear 170, 170'. The gears 170, 170' arepositioned with respect to the screen 30 so that the screen is at thepitch diameter of the gears. This insures that the screen andwork-piece, to be described, will move at the same speed with respect toeach other in a printing cycle.

The squeegee assembly 80 is mounted vertically inside the frame and isvertically reciprocable with respect to the screen. The squeegeeassembly includes a vertical holder rod 81 suitably secured to the frameby means of arm 174 thereof and carries a conventional squeegee 82 atits lower end adjacent to the screen. The squeegee holder rod 81 ispreferably spring-biased, as illustrated schematically by spring 84, sothat, when it is in printing position, it is biased toward the screen.An air cylinder 180 or the like is coupled to the squeegee assembly 80to reciprocate the assembly vertically up and down, out of and intoprinting position with respect to the screen.

The horizontally-reciprocatory table 50 is mounted beneath and inoperative relation with the screen 30 and is carried by the supporttable 110. The table 110 carries a pair of spaced-apart horizontalshafts 190, in which the table 50 is slidably supported by means ofbrackets 194 forming a portion thereof. The table 50 carries a pair ofspaced-apart vertical walls 200 which carry, on their upper surfaces,gear racks 210 which, with the gear sectors 170, form a rack and pinionarrangement. The walls 200 are positioned and dimensioned so that eachgear 210 engages one of the gear segments 170 carried by the side plates140 of frame 20. The meshing gear arrangements thus provided cause theframe 20 and table 50 to move together. Other mechanical couplingarrangements could also be used.

The apparatus includes the work-piece-carrying assembly 60 which issecured to the horizontallyreciprocatory frame and isvertically-reciprocable and carries the work-piece 70 to be screened. inone arrangement, the work-piece-carrying assembly includes a verticalpost 61 which is provided with a relatively large-diameter horizontalplate 220 at its upper end, on which the work-piece 70 is supported, anda plate 224 at its lower end. A horizontal stop plate 250, integral withtable 50, is positioned to limit the downward movement of work holder60. Similarly, a plate 228, integral with table 50, is positionedbeneath the plate 250 to limit or control the upward movement of thework-piece holder assembly at the beginning of a screening cycle, to bedescribed. Mechanical or suction means 225 is provided to hold thework-piece on the support plate 220. An air cylinder 246 is suitablycoupled to post 61 to reciprocate the work-piece assembly.

Means is provided to adjust the upward movement of the work-piece holderassembly to work-pieces of different thickness, and this means includes,in one arrangement, an assembly including a pair of wedges 230 and 240having mating sloping surfaces and adjustably coupled together by meansof spring-biased bolts 234 extending through plate 228 and into thewedges. The wedge 230 is horizontally adjustable by a micrometer 232 orthe like to set the position of the lower wedge 240, against which plate224, secured to post 61, bears as the work holder assembly 60 movesupwardly. it can be seen that adjustment of the lateral position of theinner wedge 230 sets the position of the lower wedge 240 and determinesthe maximum upward travel of the work-piece holder. It is noted thatpost 61 is journalled in plates 250 and 228, and other suitable bearingsupports may also be provided, if desired.

it is clear that other arrangements may be used to limit or adjust theupper and lower limits of motion of the work holder assembly 60. Inaddition, means (not shown) are also provided to permitthree-dimensional adjustment of the work-piece holder to compensate forany misalignments between the screen pattern and the support apparatus.

The apparatus of the invention also includes novel drive means fordriving the work-piece support apparatus 60 and the work-piece during aprinting cycle. This apparatus is suitably mounted on table and includesthree sprockets, gears, or the like 260, 262, 264, having a drive chain,cable, belt, or the like 266 secured thereto. One of the sprockets isdriven by means of a coupling to a motor 270. The chain 266 carries avertical post 274, to which a metal block 278, called a cam car", issecured. A pair of horizontal rods 280 are coupled to the cam car sothat the cam car is slidable on the rods. A generally U-shaped frame290, having a horizontal bar portion 294 and end portions 298, has theseend portions secured to the free ends of rods 280 to provide a rigidunitary assembly. The bar portion 294 is secured to the table 50 in anysuitable manner, for example, by means of a connecting post 300 suitablysecured thereto.

As illustrated in plan view in FIG. 4, the three sprockets are disposedin a triangular array, with the line b between sprockets 260 and 264representing the base of the triangle. The slope of the side S1 of thetriangle formed by the line between the sprockets 260 and 262 representsthe printing portion of the operating cycle of the invention and themovement of the cam car and the table 50. The smaller the angle betweenthe side S1 and the base b of the triangle, the slower the speed of theapparatus during the printing cycle. The side S2 of the triangle formedby the line between sprockets 262 and 264 is perpendicular to the baseb, and this represents the return travel of table 50 and frame 20, whichtakes place at maximum speed or in the shortest time. Clearly, theangles of the sprocket triangle can be arranged as desired to select thedesired relative speed of movements in each phase of operation of theapparatus. Motor 270 can also be programmed to provide the desiredrelative speeds.

The apparatus 10 also includes means for ejecting or removing a printedwork-piece 70 from support plate 220 at the end of a printing cycle andas the work table 50 and frame begin to retract and return to theirstarting position. As illustrated schematically in FIG. 5, an arm orblade 250 is positioned adjacent to the operating apparatus, eithersuitably positioned or movable into operative relation, at the end of aprinting cycle so that, as the table 50 begins to reverse its direction,the screened work-piece 70 is removed from the work holder onto asuitable support (not shown). A new work-piece can be placed on theworkpiece holder by hand or by means of suitable automatic feedapparatus, not shown.

In operation of the apparatus of the invention, initially, the table isretracted and the frame 20 is at a suitable clockwise retractedposition, clockwise as seen in FIG. 2, which places the printing pattern32 in the screen above the workpiece and in position to move toward thework-piece, as illustrated schematically in FIG. 6. At this time, thecam car 278 is moving horizontally, say, right to left along the rods280. During this period of time, with the cam car moving to the left, awork-piece 70 is placed on the table 220 of the work holder, by hand orautomatically. As the cam car turns and begins its travel along side s1of the sprocket triangle, the work table is raised into printingposition so that the work piece and screen will move into direct contactwith each other. At a suitable time, the squeegee assembly 80 is loweredinto printing position in contact with the screen, and, as illustratedschematically in FIGS. 7, 8, as the table and frame move together, theprinting pattern in the screen moves into place over and in contact withthe work-piece, and the squeegee squeezes the printing ink through thepattern onto the work-piece.

Now, the squeegee 80 is retracted, the work-piece holder 60 is lowered,and, as the cam car begins its travel along side S2 of the sprockettriangle, the printed work-piece is pushed off the table, and the frame20 and table 50 are driven quickly back to their retracted position.Again, as the cam car travels along the base of the triangle, anotherwork-piece is placed on the table, and the printing cycle can berepeated.

The apparatus of the invention has major advantages over silk-screenapparatus of the prior art and that commonly used in industry. Theprimary advantage of the invention is its speed of operation. A typicalprior art reciprocating machine performs a printing cycle in a totaltime of 4 to 6 seconds; the apparatus of the invention has operated in atotal printing cycle time of 1 second. As a result, prior art apparatus,typically, can print about 600 parts per hour, while the apparatus ofthe invention can print about 3000 parts per hour. Finally, theapparatus of the invention can be approximately 50% lower in price thantypical prior art apparatus.

The broad principles of the invention have been spelled out clearlyabove, and it is clear that many of the specific mechanical elementsdescribed can be varied or modified or replaced by others to achieve thebasic operation of the invention.

What is claimed is:

l. Silk-screen printing apparatus comprising a horizontally movablework-piece support table,

a work-piece support carried by said table,

first means coupled to said table by which said table can movehorizontally forward and backward along a predetermined path,

a rotatable screen-carrying frame rotatably mounted on a horizontalshaft disposed transverse to said predetermined path in which said tablemoves,

mechanical means directly coupling together said table and said framewhereby when said table moves along said path, said frame rotates onsaid shaft, and including driving means for driving said work-piecesupport table backward and forward in said predetermined path,

said driving means including three sprockets disposed in a commonhorizontal plane parallel to said table with their centers defining atriangle having a base, a first side, and a second side,

the base of said triangle being oriented transverse to said path whichsaid table traverses, said first side being oriented at an angle to saidpath, and said third side being oriented generally parallel to saidpath,

a drive chain threaded around said sprockets and movable along atriangular path corresponding to said triangle,

a motor coupled to one of said sprockets, and

mechanical coupling between said chain and said support table, andincluding a bracket slidably mounted thereon and slidable in a directionparallel to the base of said triangle and transverse to saidpredetermined path, said bracket exerting no force on said mechanicalcoupling and on said table when it moves in said direction parallel tothe base of said triangle,

said bracket being secured to and moving with said chain along saidtriangular path, said bracket exerting a driving force on said table inone direction along said predetermined path when it moves with saidchain along said first side of said triangle and in the oppositedirection when it moves with said chain along said second side of saidtriangle.

a screen, carrying a pattern to be printed on a workpiece, secured tosaid frame, said screen and its pattern moving with respect to saidwork-piece support when said frame and said table move with respect toeach other.

2. The apparatus defined in claim 1 and including means for raising andlowering said work-piece support.

3. The apparatus defined in claim 1 wherein said table is slidable onparallel rods oriented in the direction of said predetermined path andsaid horizontal shaft carries gears which mesh with gear racks carriedby said table.

4. The apparatus defined in claim 1 and including a vertical shaftsupporting said work-piece support, and

means coupled to said vertical shaft for moving it vertically up anddown with respect to said table into and out of a print position.

5. The apparatus defined in claim 4 and including further means engagingsaid vertical shaft for adjusting the vertical position of said verticalshaft and thus adjusting the vertical position of said work-piece holderwith respect to said screen.

1. Silk-screen printing apparatus comprising a horizontally movablework-piece support table, a work-piece support carried by said table,first means coupled to said table by which said table can movehorizontally forward and backward along a predetermined path, arotatable screen-carrying frame rotatably mounted on a horizontal shaftdisposed transverse to said predetermined path in which said tablemoves, mechanical means directly coupling together said table and saidframe whereby when said table moves along said path, said frame rotateson said shaft, and including driving means for driving said work-piecesupport table backward and forward in said predetermined path, saiddriving means including three sprockets disposed in a common horizontalplane parallel to said table with their centers defining a trianglehaving a base, a first side, and a second side, the base of saidtriangle being oriented transverse to said path which said tabletraverses, said first side being oriented at an angle to said path, andsaid third side being oriented generally parallel to said path, a drivechain threaded around said sprockets and movable along a triangular pathcorresponding to said triangle, a motor coupled to one of saidsprockets, and a mechanical coupling between said chain and said supporttable, and including a bracket slidably mounted thereon and slidable ina direction parallel to the base of said triangle and transverse to saidpredetermined path, said bracket exerting no force on said mechanicalcoupling and on said table when it moves in said direction parallel tothe base of said triangle, said bracket being secured to and moving withsaid chain along said triangular path, said bracket exerting a drivingforce on said table in one direction along said predetermined path whenit moves with said chain along said first side of said triangle and inthe opposite direction when it moves with said chain along said secondside of said triangle. a screen, carrying a pattern to be printed on awork-piece, secured to said frame, said screen and itS pattern movingwith respect to said work-piece support when said frame and said tablemove with respect to each other.
 1. Silk-screen printing apparatuscomprising a horizontally movable work-piece support table, a work-piecesupport carried by said table, first means coupled to said table bywhich said table can move horizontally forward and backward along apredetermined path, a rotatable screen-carrying frame rotatably mountedon a horizontal shaft disposed transverse to said predetermined path inwhich said table moves, mechanical means directly coupling together saidtable and said frame whereby when said table moves along said path, saidframe rotates on said shaft, and including driving means for drivingsaid work-piece support table backward and forward in said predeterminedpath, said driving means including three sprockets disposed in a commonhorizontal plane parallel to said table with their centers defining atriangle having a base, a first side, and a second side, the base ofsaid triangle being oriented transverse to said path which said tabletraverses, said first side being oriented at an angle to said path, andsaid third side being oriented generally parallel to said path, a drivechain threaded around said sprockets and movable along a triangular pathcorresponding to said triangle, a motor coupled to one of saidsprockets, and a mechanical coupling between said chain and said supporttable, and including a bracket slidably mounted thereon and slidable ina direction parallel to the base of said triangle and transverse to saidpredetermined path, said bracket exerting no force on said mechanicalcoupling and on said table when it moves in said direction parallel tothe base of said triangle, said bracket being secured to and moving withsaid chain along said triangular path, said bracket exerting a drivingforce on said table in one direction along said predetermined path whenit moves with said chain along said first side of said triangle and inthe opposite direction when it moves with said chain along said secondside of said triangle. a screen, carrying a pattern to be printed on awork-piece, secured to said frame, said screen and itS pattern movingwith respect to said work-piece support when said frame and said tablemove with respect to each other.
 2. The apparatus defined in claim 1 andincluding means for raising and lowering said work-piece support.
 3. Theapparatus defined in claim 1 wherein said table is slidable on parallelrods oriented in the direction of said predetermined path and saidhorizontal shaft carries gears which mesh with gear racks carried bysaid table.
 4. The apparatus defined in claim 1 and including a verticalshaft supporting said work-piece support, and means coupled to saidvertical shaft for moving it vertically up and down with respect to saidtable into and out of a print position.